Heterometallic cubane-like {M2Ln2} (M = Ni, Zn; Ln =, Gd, Dy) and {Ni2Y2} aggregates. Synthesis, structures and magnetic properties

Abstract

The syntheses, structural determinations and magnetic studies of tetranuclear M^IILn^III complexes (M = Ni, Zn; Ln = Y, Gd, Dy) involving an in situ compartmentalized schiff base ligand HL derived from the condensation of o-vanillin and 2-hydrazinopyridine as main ligand are described. Single-crystal X-ray diffraction reveals that all complexes are closely isostructural, with the central core composed of distorted {M₂Ln₂O₄} cubes of the formulas [Ni₂Ln₂(μ₃-OH)₂(L)₂(OAc)₄(H₂O)_3.5](ClO₄)₂·3H₂O (Ln = Y 1 and Gd 2), [Ni₂Dy₂(μ₃-OH)₂(L)₂(OAc)₅(EtOH)(H₂O)_1.5](ClO₄)·EtOH·H₂O (3) and [Zn₂Ln₂(μ₃-OH)₂(L)₂(OAc)₅(EtOH)(H₂O)](ClO₄)·2EtOH·1.5H₂O (Gd 4 and Dy 5). The Ln^III ions are linked by two hydroxo bridges and each M^II ion is also involved in a double phenoxo-hydroxo bridge with the two Ln^III ions, so that each hydroxo group is triply linked to the two Ln^III and one M^II ions. The magnetic properties of all complexes have been investigated. Ni₂Y₂ (1) has a ferromagnetic Ni^II⋯Ni^II interaction. A weak ferromagnetic Ni^II⋯Ln^III interaction is observed in the Ni₂Ln₂ complexes (Ln = Gd 2, Dy 3), along with a weak antiferromagnetic Ln^III⋯Ln^III interaction, a D zero-field splitting term for the nickel ion and a ferromagnetic Ni^II⋯Ni^II interaction. The isomorphous Zn₂Ln₂ (Ln = Gd 4, Dy 5) does confirm the presence of a weak antiferromagnetic Ln^III⋯Ln^III interaction. The Ni₂Dy₂ complex (3) does not behave as a SMM, which could result from a subtractive combination of the Dy and Ni anisotropies and an increased transverse anisotropy, leading to large tunnel splittings and quantum tunneling of magnetization. On the other hand, Zn₂Dy₂ (5) exhibits a possible SMM behavior, where its slow relaxation of magnetization is probably attributed to the presence of the anisotropic Dy^III ions.